The present invention relates to platform lift systems and, in particular, a wheelchair lift system integrated into a vehicle, such as a bus.
As the categorization of prior art to be listed below will testify, there are a number of forms of lifting and lowering mechanisms which have been designed specifically for the purpose of assisting persons confined to wheelchairs to enter and alight from vehicles, such as passenger automobiles, buses, and the like. A number of prior art devices have been designed which vary from relatively simple designs, which provide for only a single vector of motion, to those which offer a combination of motions to accomplish the purpose. One approach which has been taken by the prior art is the use of a lever or boom assembly which is attached to the roof of the vehicle and provided with suitable means for extending and retracting the boom from the interior to the exterior of the vehicle and further providing the boom assembly with means for being connected to the wheelchair to lift it into and out of the vehicle. Representative of such approaches are the assemblies which are described and illustrated in U.S. Pat. Nos. 3,656,637; 3.910,432; and 3,957,164.
Mechanisms of the foregoing type are unsatisfactory for use for the reason that they are inconvenient and time-consuming because of the problems inherent in connecting lines, hooks, and the like suspended from the boom assembly to the chair. Such mechanisms are acceptable in some instances, for instance, when used with passenger car vehicles where time considerations are not as significant, and where cost factors are such that a more elaborate and convenient mechanism is prohibitively expensive. Such methods are, however, unsatisfactory, particularly when used in common carrier-type vehicles, such as buses. In addition, overhead lifting mechanisms of this type are subject to swaying and swinging during their operation, thus giving the wheelchair passenger a very insecure feeling and, in extreme cases, threatening to either drop the chair or dump the occupant from his vehicle.
The present invention provides an alternative to boom assembly lift systems by providing a powered platform lift assembly which is integrated into a vehicle, such as a bus, and moves the wheelchair passenger in a completely safe and secure manner from a position inside the vehicle to the ground outside.
Powered platform lifting mechanisms are also known in the prior art. Innumerable tailgate truck lift mechanisms have been provided for the purpose of removing and loading extremely heavy items from the bed of a truck on which they are carried to the ground or to a dock or loading platform which is below the bed of the truck. Mechanisms of this type frequently use linkages, and track guidance systems associated with the linkages, for guiding the platform or other object to be lifted from one elevation to another. Representative of such powered lifting systems are the devices shown in U.S. Pat. Nos. 3,067,966 and 3,351,220. Such mechanisms are adapted and designed for specific lifting purposes and are not suited to the object of providing a quick, safe, convenient, and completely secure system for enabling persons in a wheelchair to enter and leave common carrier vehicles, such as buses.